1. Field
The present invention relates to the field of hot water supply systems and heating systems for domestic and industrial use.
2. Description of Related Art
Conventional water heaters sometimes fail due to moisture-caused material degradation that accumulates in the internal elements of the heater, causing materials therein to leak and lose their mechanical integrity. This form of failure often occurs when a heater is actuated for only a short period of time. Typically, when a heater has cooled, heated gases may precipitate water on the cold elements. When the heater is allowed to fully warm up, the moisture condensation is driven off by the high temperature. However, in a system with short ON cycles, a heater may never reach sufficient temperature to drive off the condensation.
Additionally, heaters that operate at short ON cycles often make inefficient use of energy. Because the inner elements of the water heater are initially cool, a certain amount of energy from the gas or electricity that is intended for heating water is consumed by heating up the internal structure of the heater. As such, frequent short operations of the heater lead to more energy being wasted by the heating of the internal elements.
In water heaters attached to a storage tank, a common method of control is to sense the temperature at a single point, either at the top or at the bottom of the storage tank. When temperature is sensed at the top, because of the stratification of hot and cold water (with hot water rising to the top of the tank), the top sensor may turn the heater OFF when the top strata of water has reached the high setpoint temperature, even when the lower portion of the tank, which may constitute a large part of the tank, is still filled with cooler water.
Alternatively, when using only a bottom sensor, the heater may be turned ON when only a small amount of cold water has entered the bottom of the storage tank. This small amount of cold water will quickly be heated to the proper temperature, resulting in a very short ON cycle of the heater.
Thus, what is desired is a control mechanism for reducing the frequency of short ON cycles and increasing the cycle time in a water heater system to improve the energy efficiency and extend the water heater's lifetime.